Synthesis, crystal structure and temperature-dependent behavior of gallogermanate tetrahydroborate sodalite |Na8(BH4)2|[GaGeO4]6

Tetrahydroborate enclathrated gallogermanate sodalite was successfully synthesized under mild hydrothermal conditions and characterized by X-ray powder diffraction and Fourier transform infrared (FTIR) spectroscopy. The crystal structure was refined in space group P4¯3n using the Rietveld method: a = 912.581(1) pm, V = 760.0(1) · 10−6 pm3, RB = 0.019. Within the sodalite cage formed by corner-sharing oxygen coordinated gallium and germanium tetrahedra, the hydrogen atoms of the enclathrated BH4− anions were refined on 8e (x, x, x) crystallographic position. The boron–hydrogen distances were restrained to 124.7 pm as calculated from the respective bond valence sums. High temperature behavior was investigated using temperature-dependent X-ray diffraction, FTIR and Raman spectroscopy and TG-DTA methods. A two-step sodalite decomposition reaction to the beryllonite analogous phase NaGaGeO4 was observed. The temperature-dependent development of the sodalite structural parameters evaluated by Rietveld analysis of the XRD data indicate a beginning transformation of the enclathrated NaBH4 at about 528 K followed by a decomposition of the sodalite framework starting at about 648 K. These findings are confirmed by the results obtained from temperature-dependent Raman and FTIR data evaluation.

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• Successful hydrothermal synthesis of Gallogermanate NaBH4 sodalite at 423 K in 4 h.
• Gallogermanate NaBH4 sodalite crystallizes in space group P4¯3n with a = 912.581 (1) pm.
• BVS calculations show a B–H distance of 124.7 pm.
• A two-step thermal decomposition to the beryllonite analogous NaGaGeO4 was observed.
• The BH4− oxidation starts at ∼530 K, followed by the framework decomposition at ∼650 K.